Bent blade clay coating



May 6, 1969 s, R, WQODHAM T Al. 3,442,684

BENT BLADE CLAY COATING Filed Nov. 27, 1965 JOHN D.COLL| NS INVENTORS A zomom m93@ zum .SAMUEL E. WODHM EUGENE BRADLEY mmnm ATTORNEY United States Patent O U.S. Cl. 117-64 4 Claims ABSTRACT F THE DISCLOSURE Method and apparatus for forming an improved clay coating on a paper substrate. The clay coating is applied with a doctor blade, specifically a bend portion of such doctor blade.

This invention relates to the application of clay coatings to substrates of paper and the like by means of an improved trailing doctor blade method and apparatus. More particularly, it relates to the production of clay coatings which are remarkably free of streaks and which permit heavier coating weights per unit area of substrate.

It is known that a major problem in applying waterbased clay coatings to paper surfaces by conventional trailing blade methods is that the edge of the relatively straight blade traps particles from the coating or the paper sheet or web, resulting in surface streaks. Streaking becomes increasingly severe as the base sheet becomes smoother. Again, maximum coat weights possible in most cases with the straight blade are limited to about 6 to 8 pounds of coating solids per 3,000 square feet of material coated.

It has now been found that a trailing blade can be so modified to overcome the disadvantages of conventional equipment, so as to achieve smoother coatings in the range of 3 to 15 pounds of coating solids per 3,000 square feet of paper stock, and, further, to enable a superior application of a second clay coating (over a previously dried first clay coating) in a double coating process. This modification includes bending or iiexing the trailing blade and bringing the 'bent portion thereof into contact with the backing roll over which the coated stock is passed on the way to a drying oven or to another coating application station. The coated stock or substrate is then passed between the backing roll and the blade with the coated surface of substrate impinging against the ibent surface rather than the edge of the blade.

Preferably-and sometimes, depending on the equipment available, criticallythe portion of the trailing blade which is unbent or straight and secured in a rigid ICC holder is disposed at an angle of from about 25 to 50 with the tangent of the backing roll at the blades trailing edge. Again, it is preferable that the blade be of spring steel or other flexible material, that it have a caliper in the range of from about 0.008 inch to 0.015 inch when it is spring steel (as in the examples hereinafter), and that it extend in its bent portion for from about 0.75 to 1.75 inches.

For a better understanding of the present invention, refe-rence should be had to the following examples and the attached schematic diagram wherein paper is shown being traveled around a rubber covered backing roll and through a clay coating formulation bath before passing a trailing doctor blade set alternatively in a normal blade position and in a bent blade position in accordance with the present invention.

Example I A conventional straight trailing doctor blade system and a bent trailing doctor blade in accordance with the present invention and as suggested by the attached drawing were to apply two dilTerent clay coating formulations to both the top and wire sides of different samples representing the same 0.008 inch Bristol board paper stock under similar operating conditions. The conditions and the resulting coat weights and coat characteristics are summarized in Table I.

All the ingredients of the coating formulations are commercially available and act in the manner suggested below:

Hydrasperse clay is a medium particle size kaolin clay with which a dispersing agent and a deocculant are mixed and which serves as a pigment;

Dow Latex 630 is a styrene-butadiene emulsion and serves as a coating adhesive;

National Starch Resyn 25-1103 is vinyl acetate emulsion and serves as a coating adhesive;

Penford Gum 280 is a low viscosity hydroxyethylated corn starch and serves as a coating adhesive;

Kelgin LV is a low viscosity sodium algnate and serves as a penetration control agent;

Calgon is sodium hexametaphosphate and serves as a dispersing agent;

Nopco ESI is a calcium stearate and serves as a lubricant and leveling agent;

Solar blue is a dyestuff; and p Ammonia serves as a protein solubilizer and pH control.

The work reported in Table I indicates that both the physical quality and the printing of bent blade coated stock are equal to or better than those achieved with conventional equipment.

TABLE I Run number A A B B C C D D Side coated- Top Wire Top Wire Top Wire Top Wire Blade position during application Straight Blade Bent Blade Straight Blade Bent Blade Coating Formulation Data:

Formulation ingredients, parts (solids basis):

Hydrasperse clay 100 100 100 100 100 100 100 100 DOW Latex 630 17. 2 17. 2 17. 2 17. 2 National Starch Resyn 25-1103.. 14. 4 14. 4 14. 4 14. 4 Penford Gum 280 2. 2. 0 2. 0 2.0 4. 8 4. 8 4.8 4. 8 Kelgin LV 0. 434 0.434 0.434 0. 434 0.434 0.434 0. 434 0.434 Calgon 0. 1 0. 1 0. l 0. 1 0. 1 0. 1 0. 1 0. l Nopco ESI, lb 4 4 4 4 4 4 4 4 Solar blue, g 3 3 3 3 3 3 3 3 Ammonia, cc 100 100 100 100 100 100 100 100 Viscosity, Brookfield, 12 r.p.m. and 110 F 15, 750 15, 750 10, 500 10, 500 3, 650 3, 650 3, 650 3, 650 olids, percent 63, 0 63. 0 62. 0 62.0 55. 5 55. 5 55. 5 55.5 Coating temperature, F 105 105 105 105 105 105 105 105 Coating pH 8. 7 8. 7 8. 7 8. 7 8. 3 8. 3 8. 3 8.3 Machine Operating Data:

Machine speed, fpm 500 500 500 500 500 500 500 500 Applicator roll speed, f.p.m 100 100 100 100 100 100 100 10o Blade setting:

.Angle with roll tangent, degrees 50 50 40 40 50 50 40 40 Extension, inches 1 1 1% 1% 1% 1% 1%, 1% Drying oven temperature, F.:

First zone 300 300 300 300 230 230 230 230 Second 7mm 300 300 300 300 230 230 230 230 Coat weight, lb./i:eam 7. 4 8. 0 9. 0 7. 0 6.5 7. 0 7. 1 7. 5 Physical Test Data Basis weight, ib` (24 x sti-500) Caliper, 0.001-inch Apparent density, lb./0.001 inf-h Sheield smoothness units* I.G.T. strike in, mm Vanceometer:

Base

60 seconds 360 seconds Printing Date-Gloss ink printing, percent gloss The lower the figure, the greater the smoothness.

Example II A number of runs were made using the bent trailing doctor blade system of the present invention and the top or felt side of different paper stocks to establish whether variations in coating formulations, and operating conditions such as blade extensions, calipers, and angles with backing roll tangents at the trailing edges of the blades affected the coating weights. The results of such runs are summarized in Table II.

All the ingredients of the coating formulations are commercially available and act in the manner suggested in Example I or below:

Hydraiine clay, Ultrawhite 90 clay, and Lustra clay are small particle size kaolin clays with which a dispersing agent and a dellocculant are mixed and which Serves as a pigment;

Rhoplex B-15 is an acrylic latext and serves as a coating adhesive;

Ethylex 2095 is a low viscosity hydroxyethylated corn starch, and serves as a coating adhesive;

, Delta protein is a soya protein;

Parez 613 is a melamine-formaldehyde resin and serves to insolubilize the coating;

Nopco C-104 is a calcium stearate and serves as a lubricant and leveling agent;

Colloid 58 l-B is a protective colloid which serves to keep the clay in suspension; and,

Ivory soap akes serve as a lubricating and leveling agent.

As indicated in Table II, the coating weights developed by the present system are greater than would have been achieved by conventional means.

TABLE II Run number E F G H I Side coated- Top Top Top & Wire Top Top Blade bent during applications Coating Formulation Data:

Formulation ingredients, lbs.:

dra

Nopco C-104 Nopco ESI- AColloid 581-B Ivory soap ilakes TABLE II-Continued' Run number E F G H l' Side Coated Top Top Top & Wire Top Top Blade bent during applications Viscosity, Brookfield, 12 r.p.n1. and 100 F.:

1st station ll, 000 11, 000 400 780 3200 2nd station.. 420 Solids, percent:

1st station 64 64 58. 7 58 52. 7 2nd station 59.8 Coating pH:

lst station 8. 2 8. 2 7. 9 8. 4 8. 5 2nd station 8.0 Machine Operating Data:

Machine speed, .p.m 375 360 900 450 700 25 36 37 40 1% n n 1% 1% Blade caliper, inches... 0. 016 0. 015 0. 008 0. 010 0. 010 Coat weight, lb./ream 19. 1 34. 4 1 13. 9 12. 0 12. 6

Oven temperature, F.:

1st zone 6th zone Blade Operation: Streaking. None None Chrome Calender Data O Oi Dryer condensate temperature, F. Steam pressure, p.s.i. Top nip roll pressure, p.l.i Bottom nip roll pressure, p Test Data:

Basis Weight, lb./ream Caliper, inch Pick, I.G.T., f.p.rn., No. 4 ink. Porosity, Sheflield... smoothness, Shetheld Gloss I. G.T. strike-in 1 Total coat weight on both sides. 2 Much loss than straight blade.

3 Super-calendered. 4 3 nips, 660 p.1.i.

The method and apparatus herein described are particularly, but not solely, adapted for use in improving the technique described in cO-pending Ser. No. 159,610, tiled Dec. 15, 1961.

What is claimed is:

1. In the formation of an improved clay coating on a paper substrate, a process comprising the step of applying an aqueous slurry `of the coating to the substrate, the step of moving the coating on the substrate between a rubber coated backing roll and a flexible spring steel doctor blade comprising a trailing edge, a bent portion in contact with the backing roll and disposed to impinge only the bent surface of the doctor blade against the coating on the substrate, and a straight portion secured in a rigid holder and disposed at an angle of from about 25 to 50 with a line tangential to the backing roll at the trailing edge.

2. The process of claim 1 wherein the blade has a caliper of from about 0.008 inch to 0.015 inch and the bent portion is from about 0.75 to 1.75 inches long.

3. In an apparatus for forming an improved clay coating on a paper substrate, in combination, a rubber covered backing roll and a flexible spring steel doctor blade comprising a trailing edge, a bent portion in contact with the backing roll and disposed to mpinge only the bent surface 60 of the doctor blade against the coating on the substrate, and a straight portion secured in a rigid holder and disposed at an angle of from about 25 to 50 with a line tangential to the backing roll at the trailing edge.

4. The apparatus of claim 3 wherein the blade has a caliper of from about 0.008 inch to 0.015 inch and the bent portion is from about 0.75 to 1.75 inches long.

References Cited UNITED STATES PATENTS 2,249,089 7/ 1941 Murray et al. 117-64 2,937,955 5/1960 Loomer 117-102 3,158,497 11/1964 Fird et al.

3,255,038 6/1966 Coghill 118-126 3,097,107 7/1963 Martinek 117-102 3,113,890 12/1963 Johnson et al. 118-126 3,158,498 11/1964 Carpenter 117-102 ALFRED L. LEAVITT, Primary Examiner.

THOMAS E. BOKAN, Assistant Examiner.

U.S. Cl. XR. 

